1. Field of the Invention
The present invention relates to a three-dimensional image display apparatus, and more particularly, to a three-dimensional image display apparatus for optically synthesizing images formed on different surfaces on a display screen so as to enable the synthesized image to appear three-dimensionally.
2. Description of the Prior Art
A three-dimensional television, hereinafter referred to as "3D-TV", is a typical example of the known dynamic three-dimensional image display apparatus. The known 3D-TV set has two TV cameras disposed at positions corresponding to each parallax of an observer's eyes (right and left). The two cameras are simultaneously operated in response to a single synchronizing signal so as to form an image on the left-hand side and the right-hand side. Then, the images are alternately reproduced on the same screen at doubling speeds by a time sharing in response to the same synchronizing signal and another synchronizing signal delayed by 1/2 vertical time. The observer sees the images through spectacles which are shut alternately against his or her left and right eyes so as to form a three-dimensional image in his or her brain. This type of 3D-TV set is disclosed in Japanese Laid-Open Patent Publications No. 62-210797, and No. 1-165293.
The known 3D-TV sets must be provided with a complicated picture-pickup and image-forming mechanism, and additionally, viewers must have special spectacles to enjoy the three-dimensional images.
Another method and apparatus are proposed for forming three-dimensional images. One example is disclosed in Japanese Laid-Open Patent Publication No. 61-279833. This known synthesizing apparatus is to synthesize two images into a single two-dimensional image. The projected image appears to be three-dimensional due to differences: in size and defocusing effects but it is one-dimensional. Another example is disclosed in Japanese Laid-Open Patent Publication No. 64-82884 relating to a synthesizing apparatus and method in which images are individually fixed at a particular position. This known expedient cannot reproduce a series of motion of images in the direction of depth. A third example is disclosed in Japanese Laid-Open Patent Publication No. 1-244734. According to this known ophthalmoscope, the resulting three-dimensional vision only derives from differences in the focusing ability of the eye and the size of an image but cannot achieve the effect of parallax which is essential for producing a three-dimensional image. The image formed by the lens is a real image, so that it is difficult to move the image-forming position beyond the size of the apparatus.
Besides the 3D-TV sets mentioned above, a holographic method is also used to form a three-dimensional video image, but there is no method which can achieve a satisfactory dynamic three-dimensional image.